The present invention relates generally to multi-speed transmissions for motor vehicles and, more particularly, to an automated manual transmission and a method of controlling automated gear shifts.
As known, automobile manufacturers are continuously striving to improve fuel efficiency. However, this effort to improve fuel efficiency, is typically offset by the need to provide enhanced comfort and convenience to the vehicle operator. For example, it is well known that manual transmissions are more fuel efficient than automatic transmissions, yet a majority of all passenger vehicles are equipped with automatic transmissions due to the increased convenience they provide.
More recently, xe2x80x9cautomatedxe2x80x9d variants of conventional manual transmissions have been developed which shift automatically without any input from the vehicle operator. Such automated transmissions typically include a plurality of power-operated actuators that are controlled by a transmission controller to shift traditional synchronized dog clutches. However, such automated transmissions have the disadvantage that there is a power interruption in the drive connection between the input shaft and the output shaft during sequential gear shifting. Power interrupted shifting results in a harsh shift feel which is generally considered to be unacceptable when compared to the smooth shift feel associated with most automatic transmissions. To overcome this problem, automated twin-clutch transmissions have been developed which can be powershifted to permit gearshifts to be made under load. Examples of such automated manual transmissions are shown in U.S. Pat. Nos. 5,966,989 and 5,890,392. While such powershift twin-clutch automated transmissions are satisfactory for their intended purpose, a need exists to develop simpler and more robust transmissions which advance the automotive transmission technology.
Accordingly, it is an object of the present invention to provide an automated transmission and a control system for permitting automatic shifting of the transmission.
This and other objects of the present invention are met by providing an automated multi-speed transmission adapted to transfer power from the engine to the driveline of a motor vehicle. The transmission includes an engine clutch operable to establish a releasable drive connection between the engine and an input shaft. The transmission also includes an output shaft adapted to transfer power to the driveline, and a synchromesh geartrain having a plurality of constant-mesh gearsets that can be selectively engaged to establish a plurality of forward and reverse speed ratio drive connections between the input shaft and the output shaft. The transmission also includes power-operated dog clutches for selectively engaging the constant-mesh gearsets, and a transmission controller for controlling coordinated actuation of the engine clutch and the power-operated dog clutches.
In accordance with the invention, the power-operated dog clutch associated with mid-range low gear is used during shifts to controllably actuate a clutch assembly for causing speed synchronization between the input shaft and the selected gear prior to engagement of its corresponding dog clutch. Similarly, the power-operated dog clutch associated with the top gear is used during shifts to controllably actuate a clutch assembly for causing speed matching between the input shaft and the selected gear prior to engagement of its corresponding dog clutch. These synchronization clutch assemblies have sufficient capacity to permit the engine clutch to remain engaged during the speed matching phase of the gear shift so as to permit non-power interrupted (xe2x80x9cpowershiftxe2x80x9d) sequential gear changes.
The first and second synchronization clutch assemblies are used to increase the speed of the input shaft during downshifts and retard the speed of the input shaft during upshifts. Therefore, selective actuation of either of these two synchronization clutch assemblies in conjunction with an appropriate control system permits upshifts and downshifts to be accomplished by engaging a slipping the appropriate clutch assembly until the input shaft speed required to engage the selected gear is reached. Once the speed is properly matched, the corresponding power-operated dog clutch is actuated to engage the selected gear.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the scope of this invention will become apparent to those skilled in the art.